In the last article, I wrote that while we see the palm up on slow motion videos of flick hucks, I don't think we need to try to put our palm up. I said I'd try to fully explain my thinking, and here is that article. Here's why the palm is "naturally" up on forehands.
The fingers are curled in our grip
If you look at the grips of the best throwers, their fingers are generally curled far forward, making a 90 degree angle (or more) with the surface of the palm.
To give some examples, here's a thumbnail image from Rowan McDonnell's excelultimate.com:
Here's a thumbnail of Travis Dunn from a Growlers highlight video:
And here's Jimmy Mickle:
For all these players, their fingers are curled forward at a right angle, or more. Their ring finger and pinky are usually curled forward the most. Give it a try—curling your fingers like this will naturally make your palm appear to be pointing very slightly up.
We throw the disc into the air
The diagrams in my previous article implied that the palm should be facing "forward", but I think more importantly, I was arguing that the wrist isn't "twisted" relative to the arm or the disc. So "forward" could mean different things depending on where our arm is and where we're pointing the disc.
We often aim hucks into the air in order to generate the flight path we're looking for. So of course, if we're aiming the disc slightly up and our wrist is un-distorted, our palm will be pointing slightly up as well. A few degrees of the "upness" of our palms (perhaps 10 degrees or so?) will come from pointing the disc into the air.
Throwing IO
Another simple mechanical reason we see the palm up on forehand hucks is that these throws are often being released IO. The lower the angle the arm is being rotated through, the more the palm will come 'up' as the arm moves in front of our body.
As an extreme example, think of a simplified bowling motion—a non-expert bowler who just holds the ball up behind their leg and then swings their arm forward past their leg, rolling the ball straight down the lane. As the bowling ball is released, their palm will be pointing forward. Then, as their arm swings up in a follow through, the palm will point towards the sky. But this is not because of something they've done with their wrist—it's purely because that's the way the palm naturally points with the arm in that position.
This still image from a Jimmy Mickle huck exemplifies the IO effect. Yes, his palm up, but at the same time, his wrist is not distorted. Instead, much of the palm being "up" comes from his arm being at such a low angle and coming up in front of him as it moves forward due to the shoulder rotation. His palm is facing "forwards", but at this point in the arm rotation, pointing "forwards" also includes a lot of pointing "up".
Before the moment of release
I think the best objection to my "palm forward" idea, and the objection that's made me think that maybe my idea is wrong, is looking at what happens before the throw is released. In my previous article, for example, I included this still shot of Max Thorne, palm definitely up:
I think there are two things going on here.
Inertia of the disc
The first thing that I think is happening is this. The 'top' two fingers (index finger and middle finger) are inside the disc, pushing it forward. The 'bottom' two fingers (ring and pinky) are not. When we start moving our arms forward, the disc has some inertia resisting that forward movement. That inertia ever-so-slightly holds back the forward progress of those top two fingers, but doesn't hold back the other two fingers, which are pulled forward more easily. This obviously turns the palm slightly up—but it's a natural result of the physics of the throwing motion, and not something that we need to try to do.
Chaos before the snap
The other factor here goes back to concepts I discussed in an earlier article on throwing forehand hucks. If we are successfully using our arm as a whip, at any moment in time, the parts of the arm that haven't yet been 'activated' should have a certain relaxation to them. I included a quote from this YouTube video on the science of whips:
Those strands right [at the end of the whip] are not in tension. Do you see that? ... It's chaos. And then, there's this moment, where they all come together [and suddenly reach their highest speed]
I think something similar is going on here. The wrist, of course, is at the end of our arm. All of the wrist rotation in a flick huck happens at the end of the arm motion, in the last moment before the disc is released, as all of the energy from further up in the arm is finally transferred into the wrist.
Remember our original question: does the wrist rotate around the axis I described in my diagrams or is the palm up during the throw? The answer is that the wrist rotation is happening in a very short timeframe, and everything that happens before it (the chaos) is more-or-less irrelevant. Before the wrist starts rotating, it should be sort-of relaxed, in order to most efficiently transfer the energy it will receive. This means that other factors, like the inertia of the disc I've described above, will temporarily play a role in determining what position our hand is in.
Let's look at a specific example. I've found this particular throw from Claire Chastain's throwing form video. As expected, we can find a moment before the throw is released where her palm is very much up:
But this doesn't say anything about how her wrist is rotating—because her wrist isn't in rotation at all at this point!
By my estimation, almost all of the wrist rotation happens in about 4 frames of video. At 60fps, that's 0.07 seconds of real time (You are definitely not seeing this clearly without watching it in super slow motion!). Here are those frames, in GIF form:
As you can see, especially in the last frame just after release, her palm is not pointing up during the moment of wrist rotation anywhere near the amount it was earlier in the throwing motion.
Looking at these images, I'm not sure my hypothesis was right that the wrist is rotating purely around its axis. (I do think that the main idea of my first article—that our grip determines the axis we rotate the disc around to minimize wobble—is still valid and important). In Claire Chastain's throw (and others I've highlighted), the palm is being turned down, so there must be other motions, whether they are in the wrist or the way the forearm is being turned. But it's also pretty clear evidence that the palm doesn't stay up throughout the throw—the palm is facing forward in the split second where the wrist is actually rotating.
Final Thoughts
So I'm not sure my original hypothesis was quite right, but I'm also not a fan of teaching 'palm up' concepts. I certainly agree that we'll see the palm facing up during the throwing motion. In my opinion, that's the result of the physics and biomechanics of a flick huck, and it's not something we need to use as a teaching cue.
If people try to force their palm to be pointing up, it's likely to be poor for their throws. First, because good throwing form requires a certain relaxation in the arm to efficiently transfer energy. And second, because different phases of the throw happen in such a short period of time — wrist rotation happens in less than 1/10th of a second. Consciously trying to control the direction of the palm over such short periods of time is likely impossible. Instead, focus on finding a great grip, developing a mechanically efficient throwing motion, and then just point the disc in the right direction—the palm stuff will come automatically.